This project is concerned with analyzing the cell-to-cell contacts and the internal organization of the synaptic membranes in the retina, using electron microscopy of thin-sectioned specimens and the freeze-fracturing technique. Experiments are designed which will help to understand the functional significance of the intramembrane differentiations in the photoreceptor cell synapses, and their role in the events of synaptic transmission. Synaptic vesicle membrane recycling will be investigated in the photoreceptor endings, using tracer techniques on the isolated eyecup of the turtle. Finally, attempts will be made to separate from the retina a highly enriched population of viable photoreceptor cells and to study the process of synaptic vesicle membrane recycling in the isolated cells, using both horseradish peroxidase as a tracer and labeling of the plasma membrane with ferritin-conjugated monovalent antibody.